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Old 09-06-2016, 06:24 PM   #11
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I have been looking into that as well and the only thing I have come up with is the lead acid batteries are pigs that don't get fat.
The alternator doesn't quit turning out voltage and the lead batteries doesn't quit accepting it whether full or not? So in my mind combining another battery bank inline after the lead acid bank leaves the house bank in parallel with the starting bank without some geek piece (sorry) that can controll the alternator to shutoff the power to the start batteries as needed and charge the house batteries while on the road without starving the start/run batteries?
In my world of piping I would call these control valves for the start batteries to allow flow in when needed and turn it off when not and regulate the flow to the house when not needed for the starting/running batteries.
There might be switches and things out there that can do it but I say keep it simple? Of course a hard wired generator only works if the genny is running and shore power only works if you actually plug into it?
Wire your genny cord and shore cord into the same contacts and your switch's are non- existent cause you have to get out to plug into shore power regardless of any fancy switches?
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Old 09-06-2016, 06:49 PM   #12
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Quote:
Originally Posted by cadillackid View Post
how does an alternator not charge house batteries well but does charge starting batteries?
-Christopher
Hey Chris.

The answer to your question lies in the differences between deep cycle and SLI (starting) batteries. They are very different in both purpose AND construction and require different methods of charging. If you want to get all the life out of your deep cycle AND get the most energy from them, they need to be charged properly.

Go back to post #4. Read the article I shared. Then, google your question and see for yourself. There is tons of material out there explaining the hows and whys.

Sorry, those are the geeky facts.

I can see I'm beginning to annoy folks. Sorry. Last post on this topic.
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Old 09-06-2016, 08:24 PM   #13
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I'll throw in a vote for a typical solar/wind/alternator charge controller. Since alternators put out ~14.7 volts you should be ok with a PWM controller. I haven't seen a charge controller that requires a blocking diode, by the way. They're smarter than that. My cheap Tracer MPPT charge controller is computer controlled and will take anything from 100 VDC to 14 VDC, convert it to the necessary charging voltage and will not allow energy to backflow. Easy peasy proper deep-cycle charging.

I also agree with not letting the alternator do the work on its own. Alternators are 'dumb' devices that can shorten the life of those all-too-expensive deep cycle batteries.
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Old 09-06-2016, 10:12 PM   #14
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I received a call back from my contact at Powerstream this afternoon. He tells me that based on my experience with their PST-PB1108 DC-DC converter/charger device, they're considering offering ruggedization as a value-add service on that product. Electrically it's really quite good; it just needs a little mechanical support if it'll be installed in a high-vibration environment. If anybody is interested in such a thing they should contact Powerstream.

Another product he recommended is PST-BC1212-15, which is a true multi-stage charger rather than a current-limited power supply as PST-PB1108 is.

Today I also called Midnite Solar to inquire about the charge controller idea. I've always had some doubt about it because PV applications are almost (or completely?) universally a step-down operation. They take a solar array with output of something like 17-600 volts and step it down to 14-ish for charging a battery bank. In contrast, this application could need to step up or down. Unfortunately Midnite had a very busy day today; a receptionist took a message from me but I didn't receive a call back yet. Maybe tomorrow.
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Old 09-07-2016, 07:26 AM   #15
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Starting to get a bit hacky, but I've had good luck coupling one of these 600w 10-60V to 12-80V step up converters connected to a treadmill motor (which is turned by a gas engine for use as a generator) then to my MPPT solar charger. The treadmill generator puts out ~60vdc when spinning. I especially wanted the 600w converter for the current limiting (which the step up converter also does), but the fact that it can step up voltage to 80vdc is useful to reduce loss through the transmission wires. As mentioned previously, the Tracer 4210rn MPPT charge controller can take up to 100vdc.

Using one of these units you could step up the alternators ~14.7vdc to ~16-20vdc or so and feed that into a PWM charge controller or, if your batteries are far from the alternator, you could increase the voltage to ~80vdc and feed it into an MPPT charge controller.
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Old 09-07-2016, 07:37 AM   #16
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Heehee.. I couldn't resist.. I just bought another one of those nifty little units to install between my bus's alternator and the MPPT charge controller. I don't drive the bus frequently and the solar has always provided enough charge.. I'm just curious now! I'll install a switch before the 600w power supply so it can be enabled or disabled.
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Old 09-09-2016, 02:59 PM   #17
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Just got off the phone with a support guy at Midnite. He explained that a PWM-style charge controller essentially connects input directly to output for a variable duration of time (thus "pulse width modulation"). The input has to be higher voltage than the output because there isn't any voltage boosting going on in there. The input also must be tolerant of having the load switched on and off. The PWM charge controller is designed to be supplied from something that inherently current-limits, so if instead it is connected to a power supply/alternator/battery that doesn't current-limit or at least doesn't as low as a solar cell would, then there's a risk of damaging the charge controller by running excessively high current pulses through it.

The MPPT is more complicated. It still doesn't have any voltage boosting going on; the input has to be higher voltage than the output. (We didn't talk about what the drop-out voltage is.) He explained that as the MPPT sweeps the amount of current it draws it expects the input voltage to drop as current rises. With a strong power supply (or battery, alternator) at the input that expected voltage drop won't happen in the way it would have with a PV input. A power supply might hit its current limit and just shut down. A battery or especially an alternator would try to supply the current without letting the voltage droop. He says it can be made to work, kind of, with the addition of series diodes and/or ballast resistors to make the input source behave a little more like a PV array would.

It made me laugh that he too suggested picking up an inexpensive inverter and mains-input battery charger..

So that's the story I got from Midnite: their charge controllers are not recommended for this use. Is there another charge controller vendor who does recommend their parts for this battery- (or alternator-) to-battery charging application?
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Old 09-09-2016, 09:40 PM   #18
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Quote:
Originally Posted by family wagon View Post
The PWM charge controller is designed to be supplied from something that inherently current-limits, so if instead it is connected to a power supply/alternator/battery that doesn't current-limit or at least doesn't as low as a solar cell would, then there's a risk of damaging the charge controller by running excessively high current pulses through it.
Yep! I needed a current limiter to connect my DC generator to my Tracer MPPT charge controller. Without one I could tell that I was burning out the generator. Things started to get real hot and sparky I set the limiter to put out around 30a@14.7vdc and it was doing well. I just need to set up a better system for tightening the v-belt that connects the engine to the generator...

I can't say I even gave it a second thought when putting DC generator power into the charge controller. It has instructions for wiring in a wind turbine, after all.
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